Friday, November 28, 2008

It's the stops

Was the problem the stops, or was it that the owner did not properly care for their bike? I understand you sweat, but can you clean it?

Also, was the problem due in part, or wholly, to the fact that you were using aero bars on the bike? Just curious."

Anonymous was referring to head tube cable stops, a recent and hopefully short-lived detail of road bike design. This photo shows the cable routing I used on the tri bike I was repairing.

Here is a photo of the typical and inevitable destruction of cable housing on a bike with head tube stops and conventional drop bars.

The aero bars on the black bike did complicate the problem, but the basic flaw affects any cabling. The curve ends too abruptly, too close to the pivot point of the whole assembly. It would only work well if the cables went into a ball swivel that allowed the ferrule to rotate freely without turning the threaded adjuster or fraying the cable over a hard edge. That's why I hate them. They make life worse in a small way and better in no way. The only way to work around them would be to remove them entirely.

The salt and sugar bath poured over the black bike only made the cable adjusters corrode into the stops. That can't be cleaned off after the fact without disassembling the bike to some degree. Salty water seeps in along the cable and down the threads of the adjuster by capillary action. Well-greased adjuster threads will guard against the damage for a while. Eventually, everything needs to be taken apart, hosed out with spray lube and put back together with fresh grease.

I suggested to the triathlete whose bike inspired my rant that she get a beater bike to stick on her trainer. Sweat on a real ride blows away on the breeze. That confines the sugar water to the vicinity of the water bottle cages and wherever the rider drools a significant amount. Much of the lip-drip blows away like the sweat. If the beater isn't an option, rig a towel or buy one of the prepared sweat catchers you can stick on your bike to catch the briny swill before it soaks anything expensive and delicate.

9 comments:

I'm wondering if you could relieve some of the stress by swapping the cable between the stops. Run the cable from the left shifter to the right stop and the right cable to the left stop, then cross the cables under the downtube. It would increase the radius of the bend in the cable housing, and perhaps would last longer than the factory setup.

I made reference to cross-routing in my earlier post. I always do it when the radius of the down tube and placement of the stops permits it, which is often not the case. Even with cross-routing, the abrupt stop at the head tube makes a stress riser at that point which cannot be relieved. Head tube cable stops are just plain bad design.

I have head tube cable stops on my Zinn. A ferrule got tweaked and caused the cable to break, stranding me with only a front derailleur many miles and several hills from home. The brass replacement ferrule seems to be sturdier, but there probably wouldn't have been a problem if the stops were on the downtube.

Give this some thought. What about using a brass ball that's been center drilled as a ferrule? It may pivot enough on the cable stop and prevent breakage. McMaster sells brass balls (no cheap jokes, please!). Go to http://www.mcmaster.com/ click on metals at the bottom of the page, then brass/balls. A dab of grease or TriFlow would help it pivot and prevent dissimilar metal corrosion.

"It would only work well if the cables went into a ball swivel that allowed the ferrule to rotate freely..."

Great minds think alike, eh? Still, I'm not sure this would not move the problem to the exit of the ferrule, where the stainless cable would get worked over a very tight edge. On my bar-end shifters I notice that the cables fail where they come off the radius of the shifter, which is much larger than the bend exiting a swiveling ferrule would be.

At this point, someone needs to do the experiment. Who's got the balls?